1. Field of the Invention
The present invention relates to a fingerprint image pickup device, and more particularly to a fingerprint image pickup device for acquiring a stable fingerprint image with better contrast, regardless of a wet state on a skin surface for fingerprint, even when the irregularities of fingerprint are obscure, whereby the performance of personal identification is improved.
2. Description of the Related Art
The conventional fingerprint image pickup device holds a finger out of contact with a fingerprint part of a fingertip portion, applies the light from the instep side (back side) of the fingertip portion and detects the light transmitted through the inside of the finger. Since the transmissivity of the light transmitted through the fingertip portion is higher in the concave part than the convex part of fingerprint, an image that is brighter in the concave part than the convex part of fingerprint is obtained (e.g., refer to JP-A-2003-85538 (pages 3 to 4, FIGS. 1 to 4)).
The conventional fingerprint image pickup device is constituted in the above way, and can acquire a stable fingerprint image, regardless of a wet state on a skin surface for fingerprint, even when the irregularities of fingerprint are obscure, but the contrast of fingerprint image is desired to be further improved.